Often times women believe cardio is the answer to fat loss. And it can certainly help if used properly. Often it is not.
Too much cardio and not enough calories equals a slower metabolism and stored fat. The basic cycle goes something like this...
- We want to lose fat
- We eat less calories (1200 is a popular number)
- We start getting serious with cardio (an hour or so a day)
- We start to lose weight on the scale
- We get happy and pat ourselves on the back
- We ease up on the cardio and start to actually eat again
- We gain weight on the scale
- We freak out and start the process over
This is called yo-yo dieting and it always ends badly. What happens when we have too much cardio and not enough calories or fuel is that we go through a process called gluconeogenesis. That means taking protein (or muscle) and breaking it down into glucose for fuel.
In other words we eat our muscle and store the fat. Many people think that when we eat less and workout we burn fat. After all the scale went down... right?
The scale may have gone down, but in most cases you simply lost water and muscle. You actually stored fat. Then when you ease up on the cardio and eat normally again... you gain all that fat back. So now you weigh more and you sent your metabolism out of whack.
Whew

Lesson here is to eat well and often. Also eat according to your goals and current situation. Many people find out how many calories they need per day and then never think to adjust it as they lose weight.
Hope that helps a bit. Side note- too much of anything and not enough cardio is bad. But more than likely women go too hard on cardio as opposed to strength training. They tend to go light on weights and hardcore on cardio. Not a good idea.